Radioactivity distribution of thorium in sediment core of the Sabah-Sarawak coast

Abstract

Thorium activity concentrations were measured in seven marine sediment cores taken from Sabah-Sarawak coast on 2004 by using a gravity box corer. Collected sediments were generally homogenous mud which contained much more mixture of silt and clay compared to sand and relatively low content of organic carbon (i.e. less than 5% at all sampling stations). The results found that activity concentrations of 230Th, 232Th and ratios of 230Th/232Th were ranged from 6.5–20.4 Bq/kg dry wt., 6.8–27.8 Bq/kg dry wt. and 0.69–0.92, respectively. It seem that, 232Th activity concentrations are slightly higher than 230Th at all sampling stations and both radionuclides were generally high at Sabah compared to Sarawak coastal waters. 230Th activity concentrations in sediment core appear to be correlated with the activity concentrations of 232Th at some sampling station. These indicating both radionuclides were supplied from the same of environment and source origin of detrital from terrestrial and shallower water. The low 230Th/232Th activity ratio which is less than unity suggesting that 232Th was actively and rapidly regenerated compared to 230Th from 234U. It also can be attributed to less efficiently scavenge of 230Th onto particles prior deposited at the marine sediment bed.